This application claims the priority benefit of Japanese application Ser. No. 2001-248202, filed on Aug. 17, 2001.
1. Field of the Invention
This invention relates generally to an image forming device. More particularly, the invention relates to an image forming device capable of improving a separation characteristic of a transfer paper in a transfer carrying device.
2. Description of Related Art
Conventionally, a staining amount on a photoreceptor in an image forming device is determined by a value, called printtac ID. For stabilizing the carrying property and improving the separation property of the transfer paper from the photoreceptor when the staining amount is the printac ID or within a certain range, the carrying property can be stabilized by only specifying the resistance of the transfer carrying belt. For example, in the Japanese Laid Open 10-213974, the separation property (carrying property) is improved by specifying the surface resistance of the transfer belt and the surface resistance of a rubber surface, so as to prevent voids from occurring on the image. In this way, the separation property is improved.
However, as the staining amount on the photoreceptor is the printac ID or below a certain critical level, the front end of the transfer paper might not be separated from the photoreceptor. For example, if the toner stained on the photoreceptor is reduced, the attraction force between the transfer paper and the photoreceptor is larger than a force that attracts the transfer paper to the transfer carrying belt. As a result, the front end of the transfer paper is attracted to the transfer carrying belt, and the transfer paper and cannot be carried by the transfer carrying belt. Therefore, there exists a problem that the transfer paper is firmly attracted onto the photoreceptor and is carried by the photoreceptor. When this phenomenon occurs, the front end of the transfer paper will come in contact with a claw on the photoreceptor, and therefore, the toner attached on the claw will adhere onto the transfer paper.
Accordingly, it is an object of the present invention to provide an image forming device, capable of solving the above problems. The separation property concerning in the present invention does not occur for all paper types, but only for some paper types. As for the method for setting the transfer paper to a paper-feeding unit (or cassette), there are four methods for setting the transfer paper: two for surfaces (front and back surfaces) of the transfer paper, and two for carrying directions of the transfer paper. Each of the four setting directions to the paper-feeding unit will arise slightly different in the strength of the transfer paper.
Accordingly, it is an object of this invention is to provide an image forming device, having a contact type transfer carrying device. The image forming device can improve the separation property of the transfer paper from an image supporter, such as a photoreceptor. In addition, an optimum separation property can be maintained according to a different separation extent from the photoreceptor due to the resistance of the transfer carrying belt.
In order to achieve the above object(s), the invention provides an image forming device, comprising an image supporter for supporting a toner image; a transfer carrying unit (for example, an endless contact type), for supporting a sheet-shaped transfer paper, and for transferring the toner image on the image supporter to the supported transfer paper; a cleaning unit for cleaning the transfer carrying unit; a unit, for stretching and laying the transfer carrying unit; a transfer bias supplying unit, for supplying a transfer bias to the transfer carrying unit; and a resistance detecting unit, for detecting a resistance of the transfer carrying unit. An applying timing for applying the transfer bias to the transfer carrying unit is at least after the transfer paper enters a nip portion between the image supporter and the transfer carrying unit, and an applying position for applying the transfer bias is within a non-image region of the transfer paper
In the above image forming device, the applying timing for applying the transfer bias to the transfer carrying unit is changeable according to the resistance detected by the resistance detecting unit.
In addition, a transfer bias, which is applied between the transfer papers, of the transfer carrying unit is changeable according to the resistance detected by the resistance detecting unit.